Accelerometers are used in a variety of applications ranging from inertial guidance systems to airbag deployment systems in modern automobiles, as well as in many other scientific and engineering systems. Commonly, an accelerometer may be micro electromechanical system (MEMS) based and available in a wide variety of acceleration sensing ranges of up to thousands of g's. In addition, single axis, dual axis, and three axis configurations are available. A proof mass beam of a MEMS based accelerometer may comprise either a simple cantilever beam or a dual compound cantilever (teeter-totter) with a fulcrum that is displaced from its center of mass. Either type of MEMS beam may be used in an open-loop or a closed-loop accelerometer system. In both open-loop and closed-loop systems, the MEMS mechanism contains a set of one or more plates to detect deflection of the proof mass beam. In closed-loop systems, the MEMS mechanism contains an additional set of two or more plates to control the position of the proof mass. These “drive” or “torque” plates are used to hold the proof mass at a relatively fixed position via attractive electrostatic forces. Such a “rebalancing” accelerometer system has an extended range of operation and minimizes distortion in the sensed acceleration.
When an accelerometer undergoes an acceleration, the deflection sensing circuity measures small changes in displacement or deflection (e.g., in a cantilever beam). A control circuit then generates a control or “torque” voltage to rebalance the proof mass and minimize its deflection. Typically, the torque driver circuit then switches this voltage to the correct plate (right or left) to assert the required force. The torque driver circuit may also amplify the torque voltage to allow operation of the control circuit at a lower voltage. This force, which continuously receives feedback via the deflection sensing circuitry, correctively balances the accelerometer. The magnitude of the voltage signals used to provide the corrective force, is then an indicator as to the magnitude and direction of acceleration that an accelerometer is undergoing.